GSM (Global System for Mobile Communications) radio coverage, which may also be referred to as second generation (2G) radio coverage, is quite extensive today. During the introduction of UMTS (Universal System for Mobile Telecommunications), which may also be referred to as third generation (3G) radio coverage, UMTS radio coverage is expected to be limited to urban areas. Thus UMTS radio coverage will cover only parts of the more extensive GSM radio coverage areas. Even within UMTS coverage areas, the UMTS radio coverage cannot be expected to be contiguous. For example, given that the frequency used for UMTS is higher than that for GSM, the in-building penetration will not be as good as GSM. This will result in small pockets (such as inside buildings) without UMTS coverage within the overall UMTS coverage area. Thus, only GSM radio coverage will be available in these pockets.
A dual mode GSM and UMTS mobile terminal (a mobile terminal is referred to as user equipment (UE) in UMTS) can communicate using either one of the two radio access systems. If a dual mode mobile terminal communicating via the UMTS radio link goes out of UMTS coverage, to an area with only GSM coverage, it can expect to continue the communication via the GSM radio link, but with a consequential degradation of service. Similarly a dual mode mobile terminal in an area with only GSM radio coverage which moves into an area with UMTS coverage can expect to switch to the UMTS radio link to improve service.
Thus as a dual mode mobile terminal moves around within radio access areas, changes in the type of radio access can be expected as the available radio access systems change. As the mobile terminal moves between radio access areas routing area updates occur to notify the necessary support network of the new position of the mobile in the routing area associated with the particular radio access type. Changing between two radio access systems involves additional signalling and can also lead to outages during the transition between the two systems. The impact of the additional signalling and outages depends on the network architecture and the protocols chosen.
In addition, if a mobile terminal operating in the 3G mode of operation moves out of 3G coverage, then there is a consequential degradation in service when communication with the 2G core network is established.
It is an object of the present invention to provide an improved network architecture suitable for an architecture in which at least two functional modes of operation exist.
The paper by Schieder A Et Al entitled ‘Gran—A New Concept for Wireless Access in UMTS’ ISS. World Telecommunications Congress. (International Switching Symposium), CA, Toronto, Pinnacle Group, 21 Sep. 1997 (1997-09-21), pages 339-345, discloses a packet switched network architecture comprising a location area connected by a radio access network to at least two core networks having different functionality, wherein the radio access network switches packet transmissions from each terminal in the location area to one of the at least two core networks.